The present invention relates, in general, to the production of ultra-short light pulses which are tunable in the infrared, and particularly to a synchronously pumped optical parametric oscillator which provides femtosecond output light pulses at a high repetition rate, the light being in the infrared wavelength band and being potentially tunable in a range of from about 0.72 to about 4.5 micrometers.
Laser pulses in the femtosecond time domain; i.e., pulses having widths of from 10.sup.-15 to 10.sup.-13 seconds, have become important tools for studying extremely short-duration events such as chemical reactions, for by directing femtosecond pulses at reacting chemicals, for example, researchers can capture spectroscopic information about the structure and behavior of short-lived molecular intermediates of the reactions. Femtosecond lasers are also important for studying the dynamics and the ultimate limits of high-speed semiconductor electronic and optical devices. However, numerous ultrafast phenomena have been inaccessible to direct optical study due to a lack of light sources having appropriate wavelengths or having other suitable characteristics such as tunability or a high repetition rate.
A particularly interesting region of optical study lies in the near- to mid-infrared, where, for example, it is possible to study carrier dynamics in most families of semiconductors as well as to do time-domain vibrational spectroscopy in many molecules. Tunable sub-picosecond pulses in various parts of the near- to mid-infrared region have been generated by a number of methods in the past, but such methods have either required amplification of a femtosecond laser followed by supercontinuum generation and seeded parametric amplification, or in one case has required a transient breakup of picosecond pulses in a parametric oscillator. However, for many experiments, especially in condensed matter, the low pulse repetition rates of all of these methods, which generally have been in the range of about 10 Hertz, although some have been as high as 8 kiloHertz, as well as the expense associated with the amplified systems, has created numerous problems.
In order to meet present needs, a tunable source of optical pulses in the near to mid infrared wavelength range is required which will permit changes in the wavelength of the light produced while maintaining a high repetition pulse rate. The narrowest possible pulse width in the femtosecond range is needed, with the narrow pulse width being maintained over a wide range of wavelengths.